This invention relates to improved methods and apparatus for obtaining well-logging information, and more particularly relates to improved methods and apparatus for transforming well-logging information into a more useful and informative format.
It is conventional practice in the search for petroleum substances residing in subsurface earth formations to drill boreholes into such formations, and to survey the earth materials along the length of the boreholes to determine possible locations therein where oil or gas may be recovered. These boreholes are normally surveyed or logged by passing a "sonde" through the borehole which contains devices capable of measuring various lithological parameters of interest, and thereafter transmitting these measurements to the surface for analysis.
In the early history of well-logging, logging measurements were relatively simple, being severely limited by factors such as logging tools and surface recovery equipment. Limitations on visible displays of such measurements were accordingly not of particular significance. However, as the art of well-logging progressed, logging tools and surface equipment have become far more complex, such that massive amounts of logging information are being generated in relatively short periods of time. This, in turn, frequently has created the need for generation of easily interpreted visible records of logging operations in correlatively short time periods.
For example, well-logging systems of the type depicted and described in U.S. patent application Ser. No. 949,592, filed Oct. 10, 1978, have been developed for simultaneously generating and transmitting to the surface complex measurements from a plurality of logging tools. Not only have such systems increased the number of parameters being simultaneously measured but, as previously noted, the rate at which these measurments are available for processing has increased tremendously. This may be due to a number of factors, including the faster rate at which the sonde is now caused to traverse the borehole and thus generate measurements, the increasingly smaller increments of borehole which must be sampled, and the statistical nature of some of the more modern logging tools.
Demand for more effective graphical displays of well-logging information has not only been created by the increased number and arrival rate of parameter measurements generated from within the borehole, but from other considerations as well. For example, as the science of log analysis continues to develop, more complex interrelationships between measured parameters are being discovered. More particularly, automated log analysis techniques have been developed which will now yield direct indications of formation compositions of interest, such as oil or shale zones.
It would thus be desirable to provide improved methods for automatically deriving both qualitative and quantitative indications of information lithology during the log or shortly thereafter from the complex logging data now being generated. It would also be desirable to effectively display these indications visibly so as to be more informative, useful and quickly recognizable from the log record. It has been found desirable, for example, to cause derived measurements to be presented in graphical form on a suitable terminal device, such as a video display of high resolution capability, wherein the various measurements are scaled appropriately and displayed with reference grid lines, lithological symbols, and alpha-numeric messages, all functionally related to these measurements.
It may also be appreciated that, due to the increased sophistication and complexity of modern well-logging data, it would be highly desirable to provide an automated process whereby this vast amount of data may be quickly analyzed during the logging operation for quantitative and qualitative indications of lithology and displayed in a simplified, easily comprehensible form, so as to permit dynamic adjustment and control of the logging process for example. More specifically, it would be desirable to provide the logging engineer with a real-time graphical display derived from the various measured earth parameters directly indicative, by means of lithological symbols, of the quantitative and qualitative composition of the formations currently being traversed by the sonde, and to generate a permanent record thereof during the logging operation or shortly thereafter.
Graphical displays of functions derived from various logging parameters have been generated in real-time during the logging operation or shortly thereafter, but have characteristically suffered from numerous serious disadvantages. First, these displays do not yield direct symbolic indications of formation lithology. Instead they rely upon interpretation and analysis of the displayed functions by a logging engineer to determine presence of formation materials of interest and their relative composition. While valid human interpretation of graphical logging parameter data may be suprisingly sophisticated, it is nevertheless often subject to error due to such factors as limited interpretative experience of the log operator and the like.
Moreover, formation composition frequently is derived from highly complex functional parameter relationships and analyses which are impossible for a human operator to derive during a logging operation. Still further, upon completion of the logging operation, a permanent record thereof will not have been generated which includes the results of the analysis in terms of graphical lithology symbols indicative of formation characteristics. Thus, it is frequently difficult to quickly locate from a logging chart, which may be many feet in length, for example, pay zones of particular interest from inspection of the displayed logging curves without additional visible interpretive aids.
Several attempts have been made to solve the problem of generating real-time logs having graphical symbols indicative of formation composition derived as a function of measured parameters. One such solution has been to provide capability for "freezing" portions of logging data derived over a selected increment of borehole during the logging operation. A portion of the incoming logging data derived over this increment is displayed on a suitable video screen or strip chart recorder for more detailed functional analysis while the additional data continues to be derived and recorded. Thus, the logging operation is not interrupted while the logging engineer performs more detailed visual analysis of data and makes appropriate adjustments in the log or notations regarding lithology. However, this attempted solution has been found unsatisfactory for numerous reasons.
First, only data from selected increments of borehole may be thus analyzed in greater detail while the logging operation continues. Furthermore, the analysis is not automated, and is therefore still subject to the hereinbefore noted human experience, speed and accuracy limitations. Thus, for example, adjustments of the logging operation in response to the analysis frequently may not be made as quickly as is desired. Moreover, at the completion of the log, a permanent record thereof has still not been created with direct graphical symbols, derived as a function of the measured parameters, correlative to formation compositions of interest over the entire logged borehole.
Even when real-time automated functional lithological analysis of logging data is attempted through modern digital processing techniques, several problems may be encountered absent the teachings of the present invention. For example, the complexity of many functional analyses of lithology often requires rapid repetitive arithmatic calculations on large arrays of logging data with high precision, through-put, and wide dynamic range, in order for such analyses to permit commercially practicable logging speeds. Moreover, again due, in part, to the immense complexity of logging data which is being processed in need of visual display, means have been sought for converting the processed data, which may include curvilinear log functions, lithological symbols, and the like, from digital form to a suitable visual peripheral display at such a rate as to not constrain logging rates. Yet, due to the hereinbefore-noted processing times heretofore required for digital logging data analysis and display, such detailed real-time lithological analysis and display of logging data during the logging operation was thought to be impracticable.
Yet another problem was frequently encountered in the prior art which heretofore frequently precluded performing lithological analysis in real-time or directly after completion of the logging operation. Such analysis often requires measurements of a plurality of logging parameters, each of which is derived at identical preselected borehole depths. However, often such required measurements may not all be generated in a single traversal of the sonde through the borehole, due to physical constraints on the number of logging tools which may be joined in tandem and the like. Thus, more than one pass of the sonde through the borehole was often required.
However, difficulty was frequently experienced in the prior art in assuring that all such measurements were, in fact, derived at the same borehole elevations, in that they were not correlatively generated on a depth-dependent basis. Moreover, even if the real-time measurements were being derived at borehole depths correlative to the historical measurements, logging systems and methods of the prior art had no known method for correlatively recording or "merging" such real-time and historical measurements during the logging operation, whereby they could thereafter be immediately processed and lithological conclusions derived therefrom. Rather, conventional logging systems would generate a recording during each pass of the sonde through the borehole, each of which was then correlatively re-recorded with the other recordings to generate a merged or "consolidated" recording or digital tape of all such measurements required for lithology analysis. Only after generation of such a merged tape was the comprehensive lithological analysis performed, frequently many hours after the derivation of the last logging measurement required for such analysis.
Other serious problems have also been encountered even in attempts to generate records of logs after completion of the logging operation having direct indications of lithology such as symbols superimposed thereupon. It has been known that digital magnetic tapes of logging measurements may be made and thereafter processed after completion of the logging operation, so as to generate functions indicative of formation composition and correlative graphical records thereof. However, it has been found that long processing times are often needed to derive the necessary functional relationships from the complex logging parameter measurements and to thereafter generate correlative electrical indications of lithology symbols suitable for a plotting or display device. These processing times have thus heretofore seriously impaired the value of historically generated logs having lithology symbols.
One reason for this, for example, is that expensive well-site personnel time and equipment are frequently "tied up" after the log operation while the enhanced log record is generated for use in determining whether a re-log of the borehole is required or the depth at which a well is to be completed. Accordingly, it will be appreciated that it is desirable to provide a system and method for automatically analyzing logging parameter measurements and generating, either during the logging operation or shortly thereafter, a permanent record of such functional analysis including direct symbolic indications of formation compositions. Moreover, it would be desirable to do so with significantly reduced data processing times so as to avoid the previously noted unnecessary and expensive tying up of personnel and equipment.
The disadvantages hereinbefore noted are overcome with the present invention, and novel methods and apparatus are provided for automatically deriving, both in real-time during a logging operation or shortly thereafter, a graphical record of the functional analysis of the well-logging parameters which includes, as a result of such analysis, direct qualitative and quantitative symbolic indications of formation composition of interest, such as shale or hydrogenous zones.